In a turbo freezing machine, a small gas turbine, or the like, a rotating machine such as a centrifugal compressor or the like is used. The rotating machine has an impeller having a disk section fixed to a rotary shaft and at which a plurality of blades are installed. As the impeller is rotated, pressure energy and velocity energy are applied to a gas.
In the impeller, when the rotary shaft is rapidly rotated, a tensile stress in the vicinity of an inner circumferential surface of a mounting hole of the impeller may increase and cause damage to the impeller. In order to prevent damage to the impeller, in Patent Literature 1, a technology for reducing the tensile stress is disclosed. The impeller of Patent Literature 1 has the mounting hole passing through a central section of the impeller. The rotary shaft is inserted into the mounting hole by fitting using a slight clearance fit or an interference fit throughout the entire inner circumferential surface. Then, a stress reduction recess configured to reduce the tensile stress is formed at the inner circumferential surface of the mounting hole.